<!DOCTYPE html>
<html lang="en">
<head>
      <meta charset="UTF-8">
      <meta name="viewport" content="width=device-width, initial-scale=1.0">
      <meta http-equiv="X-UA-Compatible" content="ie=edge">
      <title>Document</title>
      <script src="../../vue.js"></script>
</head>
<body>

            <div id="app">
                       <button @click="message=123">按钮</button>

                       {{message}}
                  </div>

                  <script>
                              
                  
                         let vm=new Vue({
                                    el: '#app',
                                    data: {

                                          message:'hello vue'
                                          
                                    },
                                    methods: {
                                          
                                    },

                              });

                              vm.$watch('message',function(newValue,oldValue){

                                      console.log(newValue,oldValue);
                              });
                        </script>
            
      
</body>
</html>